As an alternative or in addition to backlighting, displays may be provided with front lighting, used to provide direct or indirect illumination on a front side of a display area. Compared with back lighting, front lighting offers different light effects. Because of this, a variety of front-lit display techniques have been used in automotive display units.
Backlighting is normally provided through a transmissive appliqué. Liquid crystal displays may be either front lit or back lit. Front lighting is normally used without backlighting when a display area is opaque. Metal foil display areas are an example of a type of display where it is not possible to provide backlighting through an opaque display area.
It can be difficult to achieve uniform lighting in a front lit display, owing to the position of the light sources, which will usually be around the periphery of the display area. Multiple light emitting diodes or several light pipes may be mounted in front of the display area with a hoods or a mask to hide the light sources from view and to direct the emitted light towards the display area. Sometimes, smoked lens material is used to control light from the front lighting arrangement, either to even out perceived imbalances in the front illumination or to reduce the intensity of stray light directed towards the display area.
A secondary issue is front light clusters emit too much light into the cabin, lowering the contrast ratio of the illuminated display area. Additionally, the performance of front lighting can be adversely affected by bright ambient light. This is a particular issue with automotive display units, which may be used in conditions where sunlight is present in the vicinity of the display unit. When sunlight is present, it may not be possible for the driver to view alphanumeric or graphical information presented by a speedometer or engine speed (rpm) indicator of the display unit.
It is an object of the present invention to provide a more convenient front lit display, which deals with these limitations.